The invention relates to an improved support bead and electrical connector for an imaging system, and more particularly to a one piece connector which addresses the support bead and longitudinally and radially positions an electron gun within an evacuated envelope and provides electrical connection to a separate deflection electrode disposed therein.
U.S. Pat. No. 3,319,110 issued to Schlesinger on May 9, 1967, describes an electron focus projection and scanning (FPS) system which utilized a mixed field system for focusing and deflecting an electron beam. The FPS system comprises a camera tube and an external coil. The coil provides an axially directed magnetic focus field. The tube contains an electrostatic yoke or deflectron formed of pairs of interleaved horizontal and vertical deflection electrodes which are attached or formed on the interior surface of the tube envelope. The electrostatic yoke generates a rotatable, bi-axial uniform electric field orthogonal to the magnetic field generated by the coil. The crossed electric and magnetic fields constitute a "focus projection and scanning" or "FPS" cavity in the central portion of the tube envelope. An FPS system provides high image resolution, high beam current density with minimum power requirements, size and weight. Conventional all-electrostatic imaging systems have an inherently long beam system and all-magnetic imaging systems are bulky, heavy and require a large amount of power. Therefore, in applications where power requirements, size and weight are to be minimized, the FPS system is preferred. It is also desirable to design the system to be very rugged and capable of withstanding severe shock and vibration, such as are encountered in military and space exploration applications. It is known that an electron gun assembly for such a system application should have low mass, and be well centered within the tube and aligned with the longitudinal axis of the tube envelope.
One prior art electron gun 10 is shown in FIG. 1. The electron gun 10 comprises a cathode assembly 12, a control grid (G1) electrode 14 and a screen grid (G2) assembly 16. The G1 electrode 14 and the G2 assembly 16 are secured in spaced-apart relation to one another by three equally spaced glass support beads 18 (only one of which is shown). The G1 electrode 14 is a deep-drawn cup having a sidewall 20. The cathode assembly 12 is disposed within the G1 electrode 14 and spaced therefrom by a ceramic spacer 22 and a ceramic feed-through 24. An annular ceramic member 26 circumscribes the sidewall 20 of the G1 electrode 14. The ceramic member 26 is longitudinally positioned along the sidewall 20 by means of three equally spaced shims 28 (only one of which is shown) and a support ring 30. The ceramic member 26 has four asymmetrially spaced apertures 32 (only one is shown) formed therethrough. A loop-strap 34 having a separate button 36 is attached thereto is disposed between the aperature 32 in the ceramic member 26 and a conductive pattern 38 formed on the interior wall of a tube envelope 40. The conductive pattern 38 comprises one of the four identical patterns which form the electrostatic yoke (now shown). The patterns 38 comprise a metal film, such as nickel. A separate electrical connector 42 is attached between the end of the loop-strap 34 adjacent to the button 36 and a stem lead 44. Three additional (but not shown) loop-straps 34, buttons 36, and electrical connectors 42 are required to longitudinally and radially position the electron gun 10 and to make electrical connections to the four conductive patterns 38 of the electrostatic yoke. The positioning structure, comprising ceramic member 26, shims 28, support ring 30, loop-straps 34, buttons 36 and electrical connectors 42, is complex and adds undesirable mass to the electron gun 10. Additionally, the loop-straps 34, formed of a flat strip, tend to scratch the conductive patterns 38 creating metal particles and reducing the integrity of the electrical connection to the electrostatic yoke. The three-piece construction of the loop-strap 34, button 36 and electrical connector 42 adds additional cost while decreasing the precision with which the electron gun 10 is located within the tube envelope 40. Finally, the asymmetric locations of the apertures 32 in the ceramic member 26 require that the corresponding loop-straps 34 also be asymmetrically placed relative to the electron gun 10. This asymmetrical positioning tends to radially displace the electron gun 10 relative to the longitudinal axis of the tube.
Accordingly, a need exists for a simple, reliable structure that will longitudinally and radially position the electron gun in relation to the longitudinal axis of the tube without damaging the electrostatic yoke pattern on the interior wall of the tube envelope.